When crushing or grinding rock, ore, cement clinker and other hard materials, roller crushers may be used having two generally parallel rolls which rotate in opposite directions, towards each other, and which are separated by a gap. The material to be crushed is fed by gravity or choke-fed into the gap. One type of roller crusher is called high pressure grinding rollers or high pressure roller crushers. This type of roller crusher uses a crushing technique called interparticle crushing. Here, the material to be crushed or pulverised is crushed, not only by the crushing surface of the rolls, but also by particles in the material to be crushed, hence the name interparticle crushing. One example of a high pressure grinding roller is described in EP-2214898 where the gap width between the two rollers can be adjusted as well as the position within the frame of the rollers. The solution disclosed in that prior art is, however, complicated and include a very large number of hydraulic working chambers.